1. Technical Field
This invention relates generally to a method modifying a bearing surface of a sliding bearing member. More particularly, it relates to a method of adding at least one surface feature as a coating to a wear surface by selective deposition of the coating in the shape of the feature on the bearing surface.
2. Related Art
A bearing is defined in a general sense as a means of positioning one member with respect to another member in such a way that relative motion of the members is possible. The members have respective bearing surfaces which are in bearing contact with one another, typically through a lubricant which is used to promote the relative movement of the members, reduce wear of the bearing surfaces, reducing corrosion and for other purposes. The relative motion of the bearing surfaces and the bearing type are dictated by the requirements of the application of which the bearing surfaces will be a part. Bearings and bearing surfaces are designed by determining the mechanical motion and functions which they must perform, and the application requirements for life and reliability and the ambient conditions, including temperature, potential contaminants, the potential for corrosion, vibration, cyclic stresses and others.
Of particular interest are sliding bearings, in which the bearing surfaces of the bearing elements are usually separated by a thin film of coating of a lubricant such as various types of oils and greases. Sliding bearings encompass a broad range of devices in which the relative movement of the bearing elements involves sliding movement of one bearing surface over the other bearing surface. Such devices include all types of journal or sleeve bearings which are used to position a shaft or movable part in a radial direction, as well as all types of thrust bearings which are used in general to prevent movement of a rotating shaft in an axial direction and as guides for linear motion of various types. Thrust bearings vary widely in design as well, ranging from simple, flat thrust collars to complex tapered-end and pivoted-shoe (i.e., Kingsbury) bearings. Some journal and thrust bearings are designed to operate with a lubricant supply under sufficient external pressure so that the load is carried by through the pressurized fluid rather than by the hydrodynamic forces generated by the sliding motion. Other bearings move slowly enough, or intermittently, or under sufficiently light loads so that separation by a film of lubricant is not necessary for satisfactory performance and life. In this case, the surfaces are allowed to rub on each other with only the boundary-lubrication properties of the lubricant, which may comprise one or both of the bearing surfaces, or the surface properties of the bearing surfaces themselves, preventing seizure and wear. Another broad category of sliding bearing and bearing surfaces include many reciprocating piston/cylinder applications, such as the bearing comprising the drive piston/cylinder of an internal combustion engine.
Various materials are used for sliding bearings, and in particular, the bearing surfaces, including metals such as various cast iron alloys, steel alloys, aluminum alloys, copper alloys and many other metals, engineering plastics of various types, including both thermoplastic and thermoset materials, various glass or ceramic materials, wood and many other materials. Lubricants come in many forms and compositions, from various fluids, including water, oil, soaps, greases and air, to solid lubricants such as graphite, molybdenum disulfide, polytetrafluoroethylene (PTFE) and others.
Among the mechanical requirements to be considered in choosing a bearing are the load to be carried and the character of the load, the surface velocity which can be tolerated by the bearing, the ability of the bearing to tolerate misalignment, the friction when starting the bearing under a load, the power consumption of the bearing, the space requirement, the type of failure that may occur, the damping capacity, and the lubrication requirements. Factors associated with each of these mechanical requirements are well-known.
There are also typically economic and environmental requirements to be considered in the selection of bearings. In this respect, the principal economic factors are life and reliability, maintenance, ease of replacement and cost. Sliding bearings, when properly designed and when operating under reasonably uniform loading with compatible material, may have excellent longevity. As to cost, sliding bearings can frequently be produced at very small cost in mass-production quantities, but their cost can be very large, when they have to be produced in small quantities for special designs. Thus, methods of making such bearings will preferably have a minimum number of required steps and be well adapted for automation and/or high volume manufacturing methods.
As indicated above, journal bearings are one type of sliding bearing. Journal bearings are classified roughly according to the method of lubricant feed to them, as (a) non-pressurized bearings, (b) pressure-fed bearings, or (c) externally pressurized bearings. Examples of non-pressurized bearing are bushings, wick-oil bearings and oil ring bearings. Pressure-fed bearings have lubricant (i.e., oil) which is fed under pressure. A pressure-fed bearing system may include a storage tank, a pump, either a full flow or bypass-type filter or centrifuge, a cooler, a pressure regulator, a temperature regulator, supply lines to the bearings, and return lines from the bearings (which drain the lubricant from the bearings back to the tank). Examples of pressure-fed bearings include circumferential-groove, cylindrical, cylindrical overshoot, pressure, multiple groove, elliptical, elliptical overshoot, three-low, pivoted-shoe, nutcracker and partial sliding bearings. Externally pressurized bearings, such as pocket bearings and hydrostatic bearings, depend upon lubricant (i.e., oil) pressure from an external pressure source to support the bearing load. This differs from hydrodynamic bearings, which depend upon lubricant pressures generated in the lubricant film to support the load.
As indicated above, thrust bearings are a second general type of sliding bearing. The types of thrust bearings include low-speed bearings, which largely depend upon boundary lubrication, types which operate on hydrodynamic principals and externally pressurized thrust bearings. These include flat-land thrust bearings, tapered-land thrust bearings, pivoted-shoe thrust bearings or Kingsbury bearings, spring-supported flexible-plate thrust bearings, step thrust bearings and pocket thrust bearings.
Another form of a sliding bearing and associated bearing surfaces include any of a number of piston and associated cylinder liner. These include reciprocating pistons used in numerous internal combustion engines and many other applications. Reciprocating pistons and their associated cylinder housings typically require continuous lubrication of the bearing surfaces, including both the piston and cylinder sidewalls. In the associated linkages to a drive mechanism, such as a crankshaft, they also utilize still other sliding bearings, such as a wristpin and associated pin bores (i.e., a rotatable cylindrical pin in a pin bore). The wristpin is also connected to a bore in a connecting rod using a similar bearing arrangement. The connecting rod is in turn connected to the crankshaft through a sleeve bearing. These surface features are also applied to the surface of piston rings for dynamic sealing and lubrication. The piston rings are coupled with the cylinder liner. The surface patterns on the piston surface strengthen the function of piston rings; they may reduce or even eliminate the rings for low cost. All of the elements of the piston/cylinder bearing and bearings associated with the linkage require lubrication, and friction and wear properties are some of the principal design requirements.
Yet another sliding bearing arrangement is a ball and socket connection, such as is described in U.S. 462,362 to Yuhta et al. A ball having a semi-spherical bearing surface or a other curved bearing surface, is used with a mating socket having a mating bearing surface. Applications for such bearings include artificial hip joints.
Many different materials can be utilized for sliding bearings depending on the bearing type and the application and application environment. They may be made of conductive or non-conductive materials; examples of conductive materials include most metals and metal alloys, such as various iron alloys (i.e., numerous cast iron and steel compositions), copper alloys and aluminum alloys, and various composites which contain a metal or other conductive material. Non-conductive materials may include various engineering plastics, such as nylon, polytetrafluoroethylene (PTFE), ceramics, molded-fabric, wood and many other non-conductive materials. The conductive materials may be formed by numerous metalworking methods, including casting, sintering, forging and other known methods, and will frequently employ machining, grinding, polishing and other well-known finishing operations to produce the finished bearing shape and surface finish.
For all applications of these sliding bearing types, friction loss and wear are two major challenges for the bearings and bearing surfaces. This is particularly the case in harsh application environments, such as is the case with the many types of sliding bearings used in automotive vehicle applications, such as those that are subjected to reciprocal or sliding motion in engines, as well as other friction/wear systems and other motion systems. Smooth and hard surfaces are typically preferred for low wear and friction to a certain extent. However, a phenomenon frequently described as surface stiction can occur if the contacting surfaces are too smooth and the bearing surface contact area is too large. Stiction is the combination of static and friction, and it represents a physical property which must be overcome by a force in order to put an object at rest into motion. Furthermore, hard materials are frequently not suitable for use as bearing materials because they generally have low fracture toughness. The use of various hard coatings for bearing surfaces have been proposed, but they are also known to be prone to failure under high surface stress conditions due to low fracture toughness or problems associated with the adhesion of the bearing surface coating to the underlying bearing material.
The use of various raised features or projections on the bearing surface in the form of a plurality of rectangular lands, cylindrical dots and other forms have been proposed, such as those described in U.S. Pat. No. 174,331 to White, U.S. Pat. No. 259,255 to Williams, U.S. Pat. No. 1,581,394 to Dann et al., U.S. Pat. No. 3,436,129 to James, U.S. Pat. No. 5,462,362 Yuhta et al. and others. Various materials have been proposed for the raised features or projections depending on the bearing materials used, ranging from buck-horn to asbestos to PTFE to ceramics; including titanium nitride, diamond, alumina, sapphire, silicon nitride, silicon carbide, zirconia, silica and titania, to metals, such as tin, lead, zinc, cadmium and alloys of such metals. These materials have been applied by various methods to the bearing surface, ranging from the insertion of distinct plugs or studs into suitably shaped holes in the bearing surface to form the raised feature to the deposition of thin films of the raised portion materials.
However, these methods have typically been specific to a particular combination of bearing material and material used to form the raised feature or projection. Further, they frequently have required extensive preparation of the bearing surface, as by drilling, forming or otherwise preparing the bearing surface to receive the raised projection, or manual or other restrictive methods of applying the raised projections to the bearing surface. The conventional processes can only fabricate macro features on the bearing parts. The process is not sufficiently flexible and efficient for many surface designs, which require thin layers and complex surface patterns. The conventional method also put too much surface materials on the part and reduces the performance of substrate because the surface materials does not perform as good as the substrate materials.
Therefore, there remains a need for improved methods of making bearings and bearing surfaces which facilitate the application of a wide range of materials for use as raised features or projections to a wide range of bearing surface materials having a wide range of bearing surface shapes, particularly methods which c an be used to form a plurality of raised features in a single step or series of steps, and more particularly methods which may be performed using automated equipment.